In the contact lens manufacturing industry, it is well known that automated inspection of contact lenses offers the opportunity to reduce production costs while increasing product consistency. Automated systems have therefore been designed to examine and reject lenses with specific kinds of defects. The goal in such automated systems has been to inspect for all defects that are of importance in product quality control and to eliminate the need for human inspection except as needed to verify the ongoing performance of the automated system.
It is generally understood that a well-designed automated inspection system is more consistent than a human inspection system because the automated system does not suffer from fatigue, distractions, or changes in subjective inspection criteria. Also, an automated system offers the opportunity to gather a large amount of data for statistical analysis, and in that way provides a means for objective quality control. This statistical base can be the foundation for continuous improvement in both the manufacturing and inspection processes.
Lens inspection systems for contact lenses may have individual containers that carry a contact lens in a saline solution. In such systems, each hydrated lens is microscopically examined for defects, for example at the edge and optical center of the lens. One such lens inspection system is disclosed in U.S. Pat. No. 5,443,152, issued Aug. 22, 1995 to Davis. This system uses dark field illumination to inspect a hydrated lens disposed in a transparent frustoconical holder. Method steps are disclosed for inspecting various parts of the lens.
In automated lens inspection systems, minute particles of dirt or other contaminants can enter the saline solution of the lens holder or can adhere to the base of the holder. The base of the lens holder can also become scratched in the process of manufacturing. The scratches and contaminants on the lens holder and in the saline solution will appear as dark spots in the image of the contact lens. An automatic inspection system could detect these dark spots and erroneously identify them as defects in the lens. It is therefore necessary to provide a means whereby such artifacts can be ignored so that they do not affect the inspection process. The lens inspection system of the invention greatly reduces the number of such artifacts and therefore enhances the reliability of the inspection process.
An automatic contact lens inspection system must also be particularly sensitive to defects, such as minute notches or tears at the periphery of the lens. Known systems have not provided a sufficiently robust and accurate method for detecting such defects. The system of the invention employs a particularly accurate method for detecting defects at the edge of the lens.
It is also important in a lens inspection system to provide a reliable and accurate means for detecting defects at the optical center of the lens and in the color printing of an iris portion of the lens. Also, if a company logo or other reference mark is printed on the lens, the inspection system must be able to detect unacceptable defects in the printing of any such logo or mark. The inspection system of the invention achieves reliable and accurate detection of such defects by utilizing an inspection matrix of brightness values for at least two images of each lens and robust inspection algorithms. The accuracy, speed and simplicity of the automated system of the invention has not heretofore been demonstrated in the art.